Alcohol isn’t just more harmful to individuals than marijuana is; it’s more harmful to society, too. Drunken driving is a big factor in this — studies generally show that alcohol impairs driving ability much more than just about any other drug does. Alcohol also makes people aggressive, and is a factor in roughly 40 percent of violent crimes committed today.

What about a link between marijuana use and aggression? Most pot smokers will tell you that marijuana helps them relax. The popular stereotype of a heavy marijuana user is the guy stoned out of his mind on the couch, eating Funyuns and watching cartoons.

But surprisingly, research on the link between marijuana and aggression has been mixed. Marijuana seems to make most people relaxed, but it can also cause anxiety and paranoia, conditions which can occasionally manifest themselves in violent ways. There are occasional reports out of Colorado of marijuana users causing harm to themselvesor to others.

So a recent study from the Netherlands, published in the journal Psychopharmacology, attempts to put this question to bed using the gold standard of scientific research: a random controlled trial. They recruited a group of 20 heavy alcohol users (three-plus drinks a day for men, two-plus for women), 21 heavy marijuana users who smoked at least three times a week, and 20 controls who didn’t use either drug heavily at all.

They then got the alcohol users drunk until their BAC measured 0.8, the standard threshold for impairment. They got the marijuana users high, by dosing them with 300 …